Dissertations / Theses: 'Ocean wave energy harvesting'

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Giuliani, Chiara. "Alteration of ocean waves by periodic submerged structures for renewable energy extraction." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2018.

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Questa tesi si concentra sul comportamento di strutture immerse e sulla loro interazione con fenomeni ondosi oceanici allo scopo di modificarne l’ampiezza in superficie. Si suppone che queste strutture siano disposte sul fondale marino secondo schemi geometrici ricorrenti, per esempio lenti. Opportune disposizioni strutturali possono indurre un’interferenza costruttiva sulle onde di superficie, le quali presentano tipicamente un carattere pseudo-periodico nel tempo e nello spazio aumentandone così l’ampiezza. Noto che l’energia delle onde di superficie è proporzionale alla loro ampiezza, i risultati proposti in questa ricerca possono essere utilizzati per migliorare, in maniera del tutto sostenibile, l’efficienza dei dispositivi che sfruttano il moto ondoso per l’estrazione di energia rinnovabile, anche noti come energy harvesters. Per questi ultimi infatti l’efficienza della conversione dell’energia dipende dalla variazione altimetrica fra la cresta e il ventre dell’onda. Nello studio del problema, si considereranno le equazioni classiche di Navier-Stokes applicate al caso di fondali medio bassi (shallow waters). Successivamente teorie complesse per lo studio di sistemi periodici (già utilizzate in altri campi come la fisica quantistica e l’elettromagnetismo), verranno applicate per descrivere l’interazione tra le onde e il fondale periodico. Tale formulazione consentirà di progettare le strutture sul fondale capaci ottimizzare l’ampiezza dell’onda rispetto al caso di fondale indisturbato.

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Martin, Dillon Minkoff. "Hydrodynamic Design Optimization and Wave Tank Testing of Self-Reacting Two-Body Wave Energy Converter." Thesis, Virginia Tech, 2017. http://hdl.handle.net/10919/80298.

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As worldwide energy consumption continues to increase, so does the demand for renewable energy sources. The total available wave energy resource for the United States alone is 2,640 TWh/yr; nearly two thirds of the 4,000 TWh of electricity used in the United States each year. It is estimated that nearly half of that available energy is recoverable through wave energy conversion techniques. In this thesis, a two-body 'point absorber' type wave energy converter with a mechanical power-takeoff is investigated. The two-body wave energy converter extracts energy through the relative motion of a floating buoy and a neutrally buoyant submerged body. Using a linear frequency-domain model, analytical solutions of the optimal power and the corresponding power-takeoff components are derived for the two-body wave energy converter. Using these solutions, a case study is conducted to investigate the influence of the submerged body size on the absorbed power of the device in regular and irregular waves. Here it is found that an optimal mass ratio between the submerged body and floating buoy exists where the device will achieve resonance. Furthermore, a case study to investigate the influence of the submerged body shape on the absorbed power is conducted using a time-domain numerical model. Here it is found that the submerged body should be designed to reduce the effects of drag, but to maintain relatively large hydrodynamic added mass and excitation force. To validate the analytical and numerical models, a 1/30th scale model of a two-body wave energy converter is tested in a wave tank. The results of the wave tank tests show that the two-body wave energy converter can absorb nearly twice the energy of a single-body 'point absorber' type wave energy converter.
Master of Science

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Xiong, Qiuchi. "Control of Vibration Systems with Mechanical Motion Rectifier and their Applications to Vehicle Suspension and Ocean Energy Harvester." Thesis, Virginia Tech, 2020. http://hdl.handle.net/10919/98004.

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Vibration control is a large branch in control research, because all moving systems may induce desired or undesired vibration. Due to the limitation of passive system's adaptability and changing excitation input, vibration control brings the solution to change system dynamic with desired behavior to fulfill control targets. According to preference, vibration control can be separated into two categories: vibration reduction and vibration amplification. Lots of research papers only examine one aspect in vibration control. The thesis investigates the control development for both control targets with two different control applications: vehicle suspension and ocean wave energy converter. It develops control methods for both systems with simplified modeling setup, then followed by the application of a novel mechanical motion rectifier (MMR) gearbox that uses mechanical one-way clutches in both systems. The flow is from the control for common system to the control design for a specifically designed system. In the thesis, active (model predictive control: MPC), semi-active (Skyhook, skyhook-power driven damper: SH-PDD, hybrid model predictive control: HMPC), and passive control (Latching Control) methods are developed for different applications or control performance comparison on single system. The thesis also studies about new type of system with switching mechanism, in which other papers do not talk too much and possible control research direction to deal with such complicated system in vibration control. The state-space modeling for both systems are provided in the thesis with detailed model of the MMR gearbox. From the simulation, it can be shown that in the vehicle suspension application, the controlled MMR gearbox can be effective in improving vehicle ride comfort by 29.2% compared to that of the traditional hydraulic suspension. In the ocean wave energy converter, the controlled MMR WEC with simple latching control can improve the power generation by 57% compared to the passive MMR WEC. Besides, the passive MMR WEC also shows its advantage on the passive direct drive WEC in power generation improvement. From the control development flow for the MMR system, the limitation of the MMR gearbox is also identified, which introduces the future work in developing active-MMR gearbox by using an electromagnetic clutch. Some possible control development directions on the active-MMR is also mentioned at the end of the thesis to provide reference for future works.
Master of Science
Vibration happens in our daily life in almost all cases. It is a regular or irregular back and forth motion of particles. For example, when we start a vehicle, the engine will do circular motion to drive the wheel, which causes vibration and we feel wave pulses on our body when we sit in the car. However, this kind of vibration is undesirable, since it makes us uncomfortable. The car manufacture designs cushion seats to absorb vibration. This is a way to use hardware to control vibration. However, this is not enough. When vehicle goes through bumps, we do have suspension to absorb vibration transferred from road to our body. The car still experiences a big shock that makes us feel dizzy. On the opposite direction, in some cases when vibration becomes the motion source for energy harvesting, we would like to enhance it. Hardware can be helpful, since by tuning some parameters of an energy harvesting device, it can match with the vibration source to maximize vibration. However, it is still not enough due to low adaptability of a fixed parameter system. To overcome the limitation of hardware, researches begin to think about the way to control vibration, which is the method to change system behavior by using real-time adjustable hardware. By introducing vibration control, the theory behind that started to be investigated. This thesis investigates the vibration control theory application in both cases: vibration reduction and vibration enhancement, which are mentioned above due to opposite application preferences. There are two major applications of vibration control: vehicle suspension control and ocean wave energy converter (WEC) control. The thesis starts from the control development for both fields with general modeling criteria, then followed by control development with specific hardware design-mechanical motion rectifier (MMR) gearbox-applied on both systems. The MMR gearbox is the researcher designed hardware that targets on vibration adjustment with hardware capability, which is similar as the cushion seats mentioned at the beginning of the abstract. However, the MMR cannot have capability to furtherly optimize system vibration, which introduces the necessity of control development based on the existing hardware. In the suspension control application, the control strategy introduced successfully improve the vehicle ride comfort by 29.2%, which means the vehicle body acceleration has been reduced furtherly to let passenger feel less vibration. In the WEC application, the power absorbed from wave has been improved by 57% by applying suitable control strategy. The performance of improvement on vibration control has proved the effect on further vibration optimization beyond hardware limitation.

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Li, Xiaofan. "Design, Analysis and Testing of a Self-reactive Wave Energy Point Absorber with Mechanical Power Take-off." Diss., Virginia Tech, 2020. http://hdl.handle.net/10919/100800.

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Ocean wave as a renewable energy source possesses great potential for solving the world energy crisis and benefit human beings. The total theoretical potential wave power on the ocean-facing coastlines of the world is around 30,000 TWh, although cannot all be adopted for generating electricity, the amount of the power can be absorbed still can occupy a large portion of the world's total energy consumption. However, multiple reasons have stopped the ocean wave energy from being widely adopted, and among those reasons, the most important one is immature of the Power Take-off (PTO) technology. In this dissertation, a self-reactive two-body wave energy point absorber that is embedded with a novel PTO using the unique mechanism of Mechanical Motion Rectifier (MMR) is investigated through design, analysis and testing to improve the energy harvesting efficiency and the reliability of the PTO. The MMR mechanism can transfer the reciprocated bi-directional movement of the ocean wave into unidirectional rotation of the generator. As a result, this mechanism brings in two advantages towards the PTO. The first advantage it possess is that the alternating stress of the PTO is changed into normal stress, hence the reliability of the components are expected to be improved significantly. The other advantage it brings in is a unique phenomenon of engagement and disengagement during the operation, which lead to a piecewise nonlinear dynamic property of the PTO. This nonlinearity of the PTO can contribute to an expanded frequency domain bandwidth and better efficiency, which are verified through both numerical simulation and in-lab experiment. During the in-lab test, the prototyped PTO achieved energy transfer efficiency as high as 81.2%, and over 40% of efficiency improvement compared with the traditional non-MMR PTO under low-speed condition, proving the previously proposed advantage. Through a more comprehensive study, the MMR PTO is further characterized and a refined dynamic model. The refined model can accurately predict the dynamic response of the PTO. The major factors that can influence the performance of the MMR PTO, which are the inertia of the PTO, the damping coefficient, and the excitation frequency, are explored through analysis and experiment comprehensively. The results show that the increase on the inertia of the PTO and excitation frequency, and decrease on the damping coefficient can lead to a longer disengagement of the PTO and can be expressed analytically. Besides the research on the PTO, the body structure of the point absorber is analyzed. Due to the low-frequency of the ocean wave excitation, usually a very large body dimension for the floating buoy of the point absorber is desired to match with that frequency. To solve this issue, a self-reactive two-body structure is designed where an additional frequency between the two interactive bodies are added to match the ocean wave frequency by adopting an additional reactive submerged body. The self-reactive two-body structure is tested in a wave to compare with the single body design. The results show that the two-body structure can successfully achieve the frequency matching function, and it can improve more than 50% of total power absorption compared with the single body design.
Doctor of Philosophy
Ocean wave as a renewable energy source possesses great potential for solving the world energy crisis and benefit human beings. The total theoretical potential wave power on the ocean-facing coastlines of the world is around 30,000 TWh, although impossible to be all transferred into electricity, the amount of the power can be absorbed still can cover a large portion of the world's total energy consumption. However, multiple reasons have stopped the ocean wave energy from being widely adopted, and among those reasons, the most important one is immature of the Power Take-off (PTO) technology. In this dissertation, a novel two body wave energy converter with a PTO using the unique mechanism of Mechanical Motion Rectifier (MMR) is investigated through design, analysis, and testing. To improve the energy harvesting efficiency and the reliability of the PTO, the dissertation induced a mechanical PTO that uses MMR mechanism which can transfer the reciprocated bi-directional movement of the ocean wave into unidirectional rotation of the generator. This mechanism brings in a unique phenomenon of engagement and disengagement and a piecewise nonlinear dynamic property into the PTO. Through a comprehensive study, the MMR PTO is further characterized and a refined dynamic model that can accurately predict the dynamic response of the PTO is established. The major factors that can influence the performance of the MMR PTO are explored and discussed both analytically and experimentally. Moreover, as it has been theoretically hypothesis that using a two-body structure for designing the point absorbers can help it to achieve a frequency tuning effect for it to better match with the excitation frequency of the ocean wave, it lacks experimental verification. In this dissertation, a scaled two-body point absorber prototype is developed and put into a wave tank to compare with the single body structure. The test results show that through the use of two-body structure and by designing the mass ratio between the two bodies properly, the point absorber can successfully match the excitation frequency of the wave. The highest power capture width ratio (CWR) achieved during the test is 58.7%, which exceeds the results of similar prototypes, proving the advantage of the proposed design.

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Rahm, Magnus. "Ocean Wave Energy : Underwater Substation System for Wave Energy Converters." Doctoral thesis, Uppsala universitet, Elektricitetslära, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-112915.

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This thesis deals with a system for operation of directly driven offshore wave energy converters. The work that has been carried out includes laboratory testing of a permanent magnet linear generator, wave energy converter mechanical design and offshore testing, and finally design, implementation, and offshore testing of an underwater collector substation. Long-term testing of a single point absorber, which was installed in March 2006, has been performed in real ocean waves in linear and in non-linear damping mode. The two different damping modes were realized by, first, a resistive load, and second, a rectifier with voltage smoothing capacitors and a resistive load in the DC-link. The loads are placed on land about 2 km east of the Lysekil wave energy research site, where the offshore experiments have been conducted. In the spring of 2009, another two wave energy converter prototypes were installed. Records of array operation were taken with two and three devices in the array. With two units, non-linear damping was used, and with three units, linear damping was employed. The point absorbers in the array are connected to the underwater substation, which is based on a 3 m3 pressure vessel standing on the seabed. In the substation, rectification of the frequency and amplitude modulated voltages from the linear generators is made. The DC voltage is smoothened by capacitors and inverted to 50 Hz electrical frequency, transformed and finally transmitted to the on-shore measuring station. Results show that the absorption is heavily dependent on the damping. It has also been shown that by increasing the damping, the standard deviation of electrical power can be reduced. The standard deviation of electrical power is reduced by array operation compared to single unit operation. Ongoing and future work include the construction and installation of a second underwater substation, which will connect the first substation and seven new WECs.

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Leclercq, Mathilde. "Harvesting energy from the sea." Thesis, KTH, Kraft- och värmeteknologi, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-91881.

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Every marine energy source presents advantages and disadvantages. For example, they are not atthe same stage of maturity. Tidal range power is fully mature but the limited number of sitesavailable, combined with the large environmental impacts and investment costs limit itsdevelopment. The idea of artificial lagoons that will be offshore tidal range plant could create a newinterest for this technology. But for the moment, no plant of this type has been constructed yet. Tidalstream power is the next mature technology of marine energy after tidal range. Its development willrequire public subsidies but is supposed to be commercial in 2015. Systems are already indemonstration in several countries (UK, France and Canada). Wave power is less mature but it willbenefit from the development of tidal stream power and will probably be commercial in 2020. Somesystems are also in demonstration but challenges seem greater in wave power than in tidal power.Wave power conversion systems have to extract energy from the waves, even the largest ones, butat the same time resist to them. Contrary to tidal stream which has a predictable resource, waves areway less predictable and systems will have to be able to resist and valorize waves. OTEC (OceanThermal Energy Conversion) has been studied for years but it is still not mature. Its development forelectricity production needs technology research to develop cheaper and more compact systems(heat exchangers, pipes…). Air conditioning applications are developing and also require the use ofpipes and heat exchangers. Advances in this utilization could maybe help the development of OTECsystems for electricity production. Osmosis is the less mature and the most challenging technology. Atechnological breakthrough in the membrane could allow a rapid development. This breakthroughwill probably come from other sectors so it is important for the industries to get ready in order todevelop the system as soon as this technological improvement will be made.

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Greenwood, Charles. "The impact of large scale wave energy converter farms on the regional wave climate." Thesis, University of the Highlands and Islands, 2016. https://pure.uhi.ac.uk/portal/en/studentthesis/the-impact-of-large-scale-wave-energy-converter-farms-on-the-regional-wave-climate(e734db00-2108-48f9-b162-a1fc85ef61d6).html.

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Eriksson, Carolina. "Model Predictive Control of CorPower Ocean Wave Energy Converter." Thesis, KTH, Skolan för elektro- och systemteknik (EES), 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-196859.

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Wave power is currently a hot topic of research, and has shown great potential as a renewable energy source. There have been lot of progress made in developing cost eﬀective Wave Energy Converters (WECs) that can compete with other sources of energy in regard to price and electrical power. Theoretical studies has shown that optimal control can increase the generated power for idealized WECs. This thesis is done in collaboration with CorPower Ocean, and investigates the use of economic Model Predictive Control (MPC) to control the generator torque in a light, point-absorbing, heaving WEC that is currently under development. The objective is to optimize the generator torque, such that the average generated power is maximized while maintaining a small ratio between maximum and average generated power. This results in a nonconvex cost function. Due to the highly nonlinear and nonsmooth dynamics of the WEC, two controllers are proposed. The ﬁrst controller consists of a system of linear MPCs, and the second controller is a nonlinear MPC. Relevant forces acting on the WEC are identiﬁed and the system dynamics are modelled from a force perspective. The models are discretized and the controllers are implemented in Simulink. The WEC, together with the controllers, is simulated in an extensive Simulink model developed by CorPower Ocean. Several diﬀerent types of ocean waves are considered, such as its energy content and its regularity. In the majority of cases, the controllers do not increase the performance of the WEC compared to a simple, well tuned controller previously developed by CorPower Ocean. Finally, possible improvements of how to reduce existing model errors are proposed.
Vågkraft har de senaste åren visat stor potential som en ny, förnyelsebar energikälla. Det har skett många framsteg inom området med att ta fram ett robust vågkraftsverk som kan utmana andra energikällor i pris och elektrisk eﬀekt. Teoretiska studier har visat att optimal styrning kan öka den elektriska eﬀekten för idialiserade vågkraftsverk. Denna rapport är skriven i sammarbete med vågkraftföretaget CorPower Ocean, och undersöker hur ekonomisk Model Predictive Control (MPC) kan användas för att styra dämpningen i ett lätt vågkraftverk vars storlek är relativt liten våglängden. Målet är att optimera dämpningen, vridmomentet, i generatorerna så att medeleﬀekten maximeras samtidigt som toppeﬀekten minimeras, detta för att skapa ett stabilare system med mindre ﬂutuationer mellan medel- och toppeﬀekt. För att nå detta mål krävs en icke konvex kostfunktion. På grund av stora olinjäriteter och diskontinuteter i systemets dynamik utvecklas två regulatorer; ett system av linjära MPC, samt en olijär MPC. Relevanta krafter som påverkar systemet identiﬁeras och modelleras från ett kraftperspektiv. Modellerna diskretiseras, och regulatorerna implementeras och simuleras i en detaljerad Simulink modell av systemet, utvecklad av CorPower Ocean. Både regelbundna och oregelbunda vågset med varierande energiinnehåll har simuleras. Regulatorerna ökar inte vågkraftverkets prestanda jämfört med en enkel, väl inställd regulator utveklad av CorPower Ocean. Slutligen föreslås förbättringar för att minska modelfell i modellerna.

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Wang, Guangyao. "An Investigation of Phase Change Material (PCM)-Based Ocean Thermal Energy Harvesting." Diss., Virginia Tech, 2019. http://hdl.handle.net/10919/100989.

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Phase change material (PCM)-based ocean thermal energy harvesting is a relatively new method, which extracts the thermal energy from the temperature gradient in the ocean thermocline. Its basic idea is to utilize the temperature variation along the ocean water depth to cyclically freeze and melt a specific kind of PCM. The volume expansion, which happens in the melting process, is used to do useful work (e.g., drive a turbine generator), thereby converting a fraction of the absorbed thermal energy into mechanical energy or electrical energy. Compared to other ocean energy technologies (e.g., wave energy converters, tidal current turbines, and ocean thermal energy conversion), the proposed PCM-based approach can be easily implemented at a small scale with a relatively simple structural system, which makes it a promising method to extend the range and service life of battery-powered devices, e.g, autonomous underwater vehicles (AUVs). This dissertation presents a combined theoretical and experimental study of the PCM-based ocean thermal energy harvesting approach, which aims at demonstrating the feasibility of the proposed approach and investigating possible methods to improve the overall performance of prototypical systems. First, a solid/liquid phase change thermodynamic model is developed, based on which a specific upperbound of the thermal efficiency is derived for the PCM-based approach. Next, a prototypical PCM-based ocean thermal energy harvesting system is designed, fabricated, and tested. To predict the performance of specific systems, a thermo-mechanical model, which couples the thermodynamic behaviors of the fluid materials and the elastic behavior of the structural system, is developed and validated based on the comparison with the experimental measurement. For the purpose of design optimization, the validated thermo-mechanical model is employed to conduct a parametric study. Based on the results of the parametric study, a new scalable and portable PCM-based ocean thermal energy harvesting system is developed and tested. In addition, the thermo-mechanical model is modified to account for the design changes. However, a combined analysis of the results from both the prototypical system and the model reveals that achieving a good performance requires maintaining a high internal pressure, which will complicate the structural design. To mitigate this issue, the idea of using a hydraulic accumulator to regulate the internal pressure is proposed, and experimentally and theoretically examined. Finally, a spatial-varying Robin transmission condition for fluid-structure coupled problems with strong added-mass effect is proposed and investigated using fluid structure interaction (FSI) model problems. This can be a potential method for the future research on the fluid-structure coupled numerical analysis of AUVs, which are integrated with and powered by the PCM-based thermal energy harvesting devices.
Doctor of Philosophy

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Horton, Bryan. "Rotational motion of pendula systems for wave energy extraction." Thesis, Available from the University of Aberdeen Library and Historic Collections Digital Resources, 2009. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?application=DIGITOOL-3&owner=resourcediscovery&custom_att_2=simple_viewer&pid=25873.

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Li, Wei. "Numerical Modelling and Statistical Analysis of Ocean Wave Energy Converters and Wave Climates." Doctoral thesis, Uppsala universitet, Elektricitetslära, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-305870.

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Ocean wave energy is considered to be one of the important potential renewable energy resources for sustainable development. Various wave energy converter technologies have been proposed to harvest the energy from ocean waves. This thesis is based on the linear generator wave energy converter developed at Uppsala University. The research in this thesis focuses on the foundation optimization and the power absorption optimization of the wave energy converters and on the wave climate modelling at the Lysekil wave converter test site. The foundation optimization study of the gravity-based foundation of the linear wave energy converter is based on statistical analysis of wave climate data measured at the Lysekil test site. The 25 years return extreme significant wave height and its associated mean zero-crossing period are chosen as the maximum wave for the maximum heave and surge forces evaluation. The power absorption optimization study on the linear generator wave energy converter is based on the wave climate at the Lysekil test site. A frequency-domain simplified numerical model is used with the power take-off damping coefficient chosen as the control parameter for optimizing the power absorption. The results show a large improvement with an optimized power take-off damping coefficient adjusted to the characteristics of the wave climate at the test site. The wave climate modelling studies are based on the wave climate data measured at the Lysekil test site. A new mixed distribution method is proposed for modelling the significant wave height. This method gives impressive goodness of fit with the measured wave data. A copula method is applied to the bivariate joint distribution of the significant wave height and the wave period. The results show an excellent goodness of fit for the Gumbel model. The general applicability of the proposed mixed-distribution method and the copula method are illustrated with wave climate data from four other sites. The results confirm the good performance of the mixed-distribution and the Gumbel copula model for the modelling of significant wave height and bivariate wave climate.

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Magagna, Davide. "Oscillating water column wave pump : a wave energy converter for water delivery." Thesis, University of Southampton, 2011. https://eprints.soton.ac.uk/349009/.

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The research presented in this dissertation investigates the development and the performances of a new type of Wave Energy Converter (WEC) aimed to provide water delivery and energy storage in the form of potential energy. The Oscillating Water Column Wave Pump (OWCP) concept was proposed and tested through a series of experimental investigations supported by scientific theory. The OWCP was developed after an extensive study of the existing wave energy technology available, from which it emerged that the Oscillating Water Column (OWC) device could be further implemented for water delivery purposes. The existing theory of the OWC was employed to develop a mathematical theory able to describe the system wave response and water removal of the OWCP. In order to understand and validate the mathematical models of the OWCP, experimental investigations were carried out under the influence of incident linear waves in a two-dimensional (2D) and three-dimensional (3D) wave flume. The experimental equipment and methodology are outlined, including the description of wave flumes, models and data acquisition equipment. Experimental tests were used to verify the concept of the OWCP and assess its performances, investigating both the response of the device to the waves with and without water removal. In order to increase the efficiencies of delivery, array configurations of multiple OWCPs were adopted. The research demonstrated that up to 14% of the energy carried by the incoming waves can be converted into useful potential energy for a single device. Moreover a further increase of the efficiencies can be obtained with the array configuration improving the overall capability of the OWCP, for optimal separation distance between the array components. Further model tests are required to extended this research to validate the developed mathematical models as an effective prediction tool of the performances of the OWCP and further increase the efficiency of water removal that can be achieved.

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Mackay, Edward B. L. "Wave energy resource assessment." Thesis, University of Southampton, 2009. https://eprints.soton.ac.uk/79448/.

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The use of satellite altimeter data for spatial mapping of the wave resource is examined. A new algorithm for estimating wave period from altimeter data is developed and validated, which enables estimates of wave energy converter (WEC) power to be derived. Maps of the long-term mean WEC power from altimeter data are of a higher spatial resolution than is available from global wave model data. They can be used for identifying promising wave energy locations along particular stretches of coastline, before a detailed study using nearshore models is undertaken. The accuracy of estimates of WEC power from wave model data is considered. Without calibration estimates of the mean WEC power from model data can be biased of the order of 10-20%. The calibration of wave model data is complicated by non-linear dependence of model parameters on multiple factors, and seasonal and interannual changes in biases. After calibration the accuracy in the estimate of the historic power production at a site is of the order of 5%, but the changing biases make it difficult to specify the accuracy more precisely. The accuracy of predictions of the future energy yield from a WEC is limited by the accuracy of the historic data and the variability in the resource. The variability in 5, 10 and 20 year mean power levels is studied for an area in the north of Scotland, and shown to be greater than if annual power anomalies were uncorrelated noise. The sensitivity of WEC power production to climate change is also examined, and it is shown that the change in wave climate over the life time of a wave farm is likely to be small in comparison to the natural level of variability. It is shown that despite the uncertainty related to variability in the wave climate, improvements in the accuracy of historic data will improve the accuracy of predictions of future WEC yield. The topic of extreme wave analysis is also considered. A comparison of estimators for the generalised Pareto distribution (GPD) is presented. It is recommended that the Likelihood-Moment estimator should be used in preference to other estimators for the GPD. The use of seasonal models for extremes is also considered. In contrast to assertions made in previous studies, it is demonstrated that non-seasonal models have a lower bias and variance than models which analyse the data in separate seasons.

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Thorburn, Karin. "Electric Energy Conversion Systems : Wave Energy and Hydropower." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-7081.

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Xu, Xu. "Nonlinear dynamics of parametric pendulum for wave energy extraction." Thesis, University of Aberdeen, 2005. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=189414.

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A new concept, extracting energy from sea waves by parametric pendulor, has been explored in this project. It is based on the conversion of vertical oscillations to rotational motion by means of a parametrically-excited pendulor, i.e. a pendulum operating in rotational mode. The main advantage of this concept lies in a direct conversion from vertical oscillations to rotations of the pendulum pivot. This thesis, firstly, reviewed a number of well established linear and nonlinear theories of sea waves and Airy’s sea wave model has been used in the modelling of the sea waves and a parametric pendulum excited by sea waves. The third or fifth order Stokes’s models can be potentially implemented in the future studies. The equation of motion obtained for a parametric pendulum excited by sea waves has the same form as for a simple parametrically-excited pendulum. Then, to deepen the fundamental understanding, an extensive theoretical analysis has been conducted on a parametrically-excited pendulum by using both numerical and analytical methods. The numerical investigations focused on the bifurcation scenarios and resonance structures, particularly, for the rotational motions. Analytical analysis of the system has been performed by applying the perturbation techniques. The approximate solutions, resonance boundary and existing boundary of rotations have been obtained with a good correspondence to numerical results. The experimental study has been carried out by exploring oscillations, rotations and chaotic motions of the pendulum.

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Waters, Rafael. "Energy from Ocean Waves : Full Scale Experimental Verification of a Wave Energy Converter." Doctoral thesis, Uppsala universitet, Elektricitetslära, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-9404.

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A wave energy converter has been constructed and its function and operational characteristics have been thoroughly investigated and published. The wave energy converter was installed in March of 2006 approximately two kilometers off the Swedish west coast in the proximity of the town Lysekil. Since then the converter has been submerged at the research site for over two and a half years and in operation during three time periods for a total of 12 months, the latest being during five months of 2008. Throughout this time the generated electricity has been transmitted to shore and operational data has been recorded. The wave energy converter and its connected electrical system has been continually upgraded and each of the three operational periods have investigated more advanced stages in the progression toward grid connection. The wave energy system has faced the challenges of the ocean and initial results and insights have been reached, most important being that the overall wave energy concept has been verified. Experiments have shown that slowly varying power generation from ocean waves is possible. Apart from the wave energy converter, three shorter studies have been performed. A sensor was designed for measuring the air gap width of the linear generator used in the wave energy converter. The sensor consists of an etched coil, a search coil, that functions passively through induction. Theory and experiment showed good agreement. The Swedish west coast wave climate has been studied in detail. The study used eight years of wave data from 13 sites in the Skagerrak and Kattegatt, and data from a wave measurement buoy located at the wave energy research site. The study resulted in scatter diagrams, hundred year extreme wave estimations, and a mapping of the energy flux in the area. The average energy flux was found to be approximately 5.2 kW/m in the offshore Skagerrak, 2.8 kW/m in the near shore Skagerrak, and 2.4 kW/m in the Kattegat. A method for evaluating renewable energy technologies in terms of economy and engineering solutions has been investigated. The match between the technologies and the fundamental physics of renewable energy sources can be given in terms of the technology’s utilization. It is argued that engineers should strive for a high utilization if competitive technologies are to be developed.

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Abraham, Edo. "Optimal control and robust estimation for ocean wave energy converters." Thesis, Imperial College London, 2013. http://hdl.handle.net/10044/1/12197.

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This thesis deals with the optimal control of wave energy converters and some associated observer design problems. The first part of the thesis will investigate model predictive control of an ocean wave energy converter to maximize extracted power. A generic heaving converter that can have both linear dampers and active elements as a power take-off system is considered and an efficient optimal control algorithm is developed for use within a receding horizon control framework. The optimal control is also characterized analytically. A direct transcription of the optimal control problem is also considered as a general nonlinear program. A variation of the projected gradient optimization scheme is formulated and shown to be feasible and computationally inexpensive compared to a standard nonlinear program solver. Since the system model is bilinear and the cost function is not convex quadratic, the resulting optimization problem is shown not to be a quadratic program. Results are compared with other methods like optimal latching to demonstrate the improvement in absorbed power under irregular sea condition simulations. In the second part, robust estimation of the radiation forces and states inherent in the optimal control of wave energy converters is considered. Motivated by this, low order H∞ observer design for bilinear systems with input constraints is investigated and numerically tractable methods for design are developed. A bilinear Luenberger type observer is formulated and the resulting synthesis problem reformulated as that for a linear parameter varying system. A bilinear matrix inequality problem is then solved to find nominal and robust quadratically stable observers. The performance of these observers is compared with that of an extended Kalman filter. The robustness of the observers to parameter uncertainty and to variation in the radiation subsystem model order is also investigated. This thesis also explores the numerical integration of bilinear control systems with zero-order hold on the control inputs. Making use of exponential integrators, exact to high accuracy integration is proposed for such systems. New a priori bounds are derived on the computational complexity of integrating bilinear systems with a given error tolerance. Employing our new bounds on computational complexity, we propose a direct exponential integrator to solve bilinear ODEs via the solution of sparse linear systems of equations. Based on this, a novel sparse direct collocation of bilinear systems for optimal control is proposed. These integration schemes are also used within the indirect optimal control method discussed in the first part.

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Du, Plessis Jacques. "A hydraulic wave energy converter." Thesis, Stellenbosch : Stellenbosch University, 2012. http://hdl.handle.net/10019.1/19950.

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Thesis (MScEng)--Stellenbosch University, 2012.
ENGLISH ABSTRACT: As a renewable energy source, wave energy has the potential to contribute to the increasing global demand for power. In South Africa specifically, the country’s energy needs may easily be satisfied by the abundance of wave energy at the South-West coast of the country. Commercially developing and utilizing wave energy devices is not without its challenges, however. The ability of these devices to survive extreme weather conditions and the need to achieve cost-efficacy while achieving high capacity factors are but some of the concerns. Constant changes in wave heights, lengths and directions as well as high energy levels and large forces during storm conditions often lead to difficulties in keeping the complexity of the device down, avoiding over-dimensioning and reaching high capacity factors. The point absorber device developed as part of this research is based on an innovation addressing the abovementioned issues. An approach is followed whereby standard "offthe- shelf" components of a proven hydraulics technology are used. The size of the device is furthermore adaptable to different wave climates, and the need for a control system is not necessary if the design parameters are chosen correctly. These characteristics enable low complexity of the device, excellent survivability and an exceptionally high capacity factor. This may lead to low capital as well as low operationand maintenance costs. In this paper the working principle of this concept is presented to illustrate how it utilises the available wave energy in oceans. The results obtained from theoretical tests correlate well with the experimental results, and it is proven that the device has the ability to achieve high capacity factors. As the device makes use of existing, "off-the-shelf" components, cost-efficient energy conversion is therefore made feasible through this research.
AFRIKAANSE OPSOMMING: As ’n hernubare/ herwinbare energiebron bied golfenergie die potensiaal om by te dra tot die bevrediging van die stygende globale energie-navraag. In spesifiek Suid-Afrika kan die oorvloed van beskikbare golfenergie aan die Suid-Weskus van die land gebruik word om aan die land se energiebehoeftes te voldoen. Betroubaarheid en oorlewing in erge weerstoestande, koste-effektiwiteit en die behaal van hoë kapasiteitsfaktore is beduidende struikelblokke wat oorkom moet word in die poging om ’n golfenergie-omsetter wat kommersieël vervaardig kan word, te ontwikkel. Daarby dra voortdurende veranderings in golfhoogtes, -lengtes en -rigtings sowel as hoë energievlakke en groot kragte tydens storms by to die feit dat dit moeilik is om die kompleksiteit van die stelsel laag te hou. Dit terwyl daar voorkom moet word dat die toestel oorontwerp en verhoed word dat hoë kapsiteitsfaktore bereik word. Die puntabsorbeerder-toestel wat in hierdie navorsing ontwikkel is, bestaan uit ’n ontwerp wat spesifiek ontwikkel is om die bogenoemde probleme aanspreek. ’n Unieke benadering is gevolg waardeur standaard, maklik-bekombare komponente gebruik is en die komponent-groottes ook aangepas kan word volgens golfgroottes. Indien die ontwerpsdimensies akkuraat gekies word, is die moontlikheid verder goed dat ’n beheerstelsel nie geïmplementeer hoef te word nie. Hierdie eienskappe verseker lae stelselkompleksiteit, uitstekende oorlewingsvermoë en ’n uitstaande kapasiteitsfaktor. Lae kapitaal- sowel as onderhoudskostes is dus moontlik. Die doel van hierdie dokument is om die werking van die konsep voor te stel en teoreties sowel as prakties te evalueer. Die resultate van teoretiese toetse stem goed ooreen met eksperimentele resultate, en dit is duidelik dat die toestel hoë kapasiteitsfaktore kan behaal. Aangesien die toestel verder gebruik maak van bestaande komponente wat alledaags beskikbaar is, word die koste-effektiewe omsetting van golfenergie dus moontlik gemaak deur hierdie navorsing.

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Curran, R. "Utilisation of the Wells turbine for wave energy conversion." Thesis, Queen's University Belfast, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.318884.

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Kanagaraj, Gireesha. "Modelling of the Novi Ocean Wave Energy Converter using WEC-Sim." Thesis, Uppsala universitet, Institutionen för elektroteknik, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-445865.

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Garcia, Teran Jessica. "Positional Analysis of Wave Power : Applied at the Pacific Ocean in Mexico." Thesis, Uppsala universitet, Institutionen för geovetenskaper, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-195854.

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The energy transition has started. The key is to find an alternative to uneconomical and unsustainable energy production. In this sense it is a challenge to develop renewable energy technologies suitable for the present and proper for the future. Uppsala University is driving the Lysekil project at its Division of Electricity. The aim is to design an environmentally friendly energy system with wave energy converters (WECs) that are simple and strong in design. However, little has been done to know more about its economically feasibility and the social impact of its benefits. Therefore, this research focuses on a positional analysis of a 3 MW Wave Power Park to understand the relevant aspects of implementing this kind of technology. The target area will be at Rosarito, Baja California at the Pacific Ocean in the Northeast of Mexico, a region experiencing increasing energy demand. This thesis combines technical, economical and social aspects. The technical part describes how the device works. The analysis is complemented by describing the current energy situation in Mexico and the social benefits of sustainable energy. Finally, the economical analysis is presented, it is focused on the perspective of the Merchant Power Plant. The review shows that wave power could be economically viable due to its high degree of utilisation. Energy diversification and security, economic and sustainable development, and clean energy are some of the advantages of wave power. Therefore, wave power is an interesting alternative for generating electricity in Mexico. However, the energy sector is highly subsidised, making it difficult for new technologies to enter the market without government participation. Another finding is that in the long run if the equipment cost decreases or subsidies are applied, the technology might be successfully implemented. Environmental consequences are described briefly, concluding that little is known and more research is needed. The environmental constraints, economic implications and uncertainties of a high energy future are disturbing. In that sense, renewable energy appears to be unequivocally better than rely to a greater extent on fossil fuels, in the sense that they offer a sustainable development and less environmental damage.

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Sarmah, Biki. "Optimisation of Electromechanical Drivetrain for Wave Energy Converter at CorPower Ocean AB." Thesis, KTH, Fordonsdynamik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-234838.

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The potential of wave energy has been constantly explored in past couple of years. The contribution from the CorPower Ocean AB towards the development of wave energy is important. This thesis involves the detailed study of current ½ scale (1:2) model of a Wave Energy converter (WEC) and computing the results to find the optimised component ratings. The primary goal of the thesis is to optimise each component of the electro-mechanical drivetrain with the assistance of modelling software Simulink and Matlab. In the initial stage of this thesis the generator and drive component are analysed without changing the drivetrain configuration of the WEC. A method is established to find suitable ratings of generator and drive system for the WEC which provides high system efficiency and power output. The method is developed in such a way that it can be implemented for any scale model whether it is full-scale or half-scale. Once finding the optimised ratings of generator and drive combination, different configuration of the drivetrain is explored for the WEC. The influence of drivetrain mechanism with and without flywheel is also considered and compared with the ½ scale model. The drivetrain configurations comprise of single generator, double generator and quadruple generator alignment with the WEC. All configurations of the generator are compared with and without a flywheel in the drivetrain. The benefit of including a flywheel involves power smoothing, control simplification and reducing component volume, whereas the benefit of not including flywheel includes better hydrodynamic damping and control. The outcome of the results showcase that the existing ½ scale WEC model can provide better performance when the generator ratings are reduced because of low speed at small sea state. The speed-ratio of the gearbox can either be increased or a new system can be introduced which chooses the generator rating depending on the sea state and motion profile. Based on the analysis result of an optimised ½ scale model, the full scale drivetrain component ratings are introduced with a different drivetrain topology. Results from the Full scale WEC model showcase that a double generator WEC configuration without a flywheel is a reliable and efficient solution for CorPower Ocean AB.

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Banerjee, S. "Ocean energy assessment : an integrated methodology." Thesis, Coventry University, 2011. http://curve.coventry.ac.uk/open/items/16196d0d-e671-489a-ba71-f20cdb6c8df3/1.

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The huge natural energy resources available in the world’s oceans are attracting increasing commercial and political interest. In order to evaluate the status and the degree of acceptability of future Ocean Energy (OE) schemes, it was considered important to develop an Integrated Assessment Methodology (IAM) for ascertaining the relative merits of the competing OE devices being proposed. Initial studies included the gathering of information on the present status of development of the ocean energy systems on wave, OTEC and tidal schemes with the challenges faced for their commercial application. In order to develop the IAM, studies were undertaken for the development and standardization of the assessment tools focussing on: • Life Cycle Assessment (LCA) on emission characteristics. • Energy Accounting (EA) studies. • Environmental Impact Assessment (EIA) over different environmental issues. • Resource captures aspects. • Defining economy evaluation indices. The IAM developed from such studies comprised of four interrelated well defined tasks and six assessment tools. The tasks included the identification of the modus operandi on data collection to be followed (from industry) for assessing respective OE devices, and also advancing relevant guidelines as to the safety standards to be followed, for their deployment at suitable sites. The IAM as developed and validated from case studies in ascertaining relative merits of competing OE devices included: suitable site selection aspects with scope for resource utilisation capability, safety factors for survivability, scope for addressing global warming & energy accounting, the environmental impact assessment both qualitatively and quantitatively on different environmental issues, and the economic benefits achievable. Some of the new ideas and concepts which were also discovered during the development of the IAM, and considered useful to both industry and researchers are given below: • Relative Product Cost (RPC) ratio concept- introduced in making an economic evaluation. This is considered helpful in sensitivity analysis and making design improvements (hybridising etc) for the cost reduction of OE devices. This index thus helps in making feasibility studies on R&D efforts, where the capital cost requirement data and life span of the device is not well defined in the primary stages of development. • Determination of the threshold limit value of the barrage constant - considered useful in determining the efficacy of the planning process. The concept ascertained the relative efficiency achieved for various barrage proposals globally. It could also be applied to suggest the revisions required for certain barrage proposals and also found useful in predicting the basin area of undefined barrage proposal for achieving economic viability. • Estimations made on the future possibility of revenue earnings from the by-products of various OTEC types, including the scope of chemical hubs from grazing type OTEC plants. • Determination of breakeven point- on cost versus life span of wave and OTEC devices studied, which is useful in designing optimum life of the concerned devices. The above stated multi-criterion assessment methodology, IAM, was extended leading to the development of a single criterion model for ascertaining sustainability percent achievable from an OE device and termed IAMs. The IAMs was developed identifying 7 Sustainability Development Indices (SDI) using some the tools of the IAM. A sustainability scale of 0-100 was also developed, attributing a Sustainability Development Load Score (SDLS) percentage distribution pattern over each SDIs, depending on their relative importance in achieving sustainability. The total sum of sustainability development (SD) gained from each SDI gave the IAMs (for the concerned device), indicating the total sustainable percentage achieved. The above IAMs developed, could be applied in ranking OE devices alongside the unsustainable coal power station. A mathematical model of estimating the IAMs was formulated, in order to ascertain the viability to the sustainable development of any energy device. The instruments of IAM and IAMs which have been developed would be helpful to the OE industry in ascertaining the degree of acceptability of their product. In addition it would also provide guidelines for their safe deployment by assessing the relative merits of competing devices. Furthermore, IAM and IAMs would be helpful to researchers undertaking feasibility studies on R&D efforts for material development research, ‘hybridization studies’ (as also new innovations), cost reduction, the performance improvement of respective devices, and any economic gains. With future advancements in OE systems and the availability of field data from large scale commercial applications, the specific values/data of the IAM & IAMs may be refined, but the logic of the models developed in this research would remain the same.

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Carter, Caroline Jane. "Tidal energy, underwater noise & marine mammals." Thesis, University of the Highlands and Islands, 2008. https://pure.uhi.ac.uk/portal/en/studentthesis/tidal-energy-underwater-noise-and-marine-mammals(9963d662-76e1-4e70-a3ac-e18a96b23101).html.

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Sourcing energy from renewable sources is currently a key theme in modern society. Consequently, the pace of development of these emerging technologies is likely to increase in the near future, particularly in marine renewables. However, the environmental and ecological impact of many of these new developments in the marine environment is largely unknown. My thesis has focused on one unknown area of interaction; the potential effect of tidal-stream devices on marine mammals. Collision risk is often cited as a key concern. Therefore, my premise was - for marine mammals to avoid a collision with a marine renewable device (assuming they are on a collision course) they must first detect the device. It is well understood that marine mammals use sound and hearing as their primary sense for communication, foraging, navigation and predator avoidance, so it is highly likely that the primary cue for device detection will be acoustic. However, it is not known how operational marine renewable devices might modify the acoustic landscape in these areas, or whether they will be audible to marine mammals in time to alert them to the presence of devices. It has been suggested that the high level of natural and anthropogenic background noise in tidal-stream areas may mask (drown out) the signal of the tidal devices. The acoustic characteristics of underwater noise in shallow coastal waters are currently not well known. My thesis adds data to this knowledge gap by measuring and mapping underwater noise levels in tidal-stream areas.

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Nie, Zanxiang Jack. "Emulation and power conditioning of outputs from a direct drive linear wave energy converter." Thesis, University of Cambridge, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.609008.

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Bracewell, Rob. "FROG and PS FROG : a study of two reactionless ocean wave energy converters." Thesis, Lancaster University, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.301820.

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Tokić, Grgur. "Optimal configuration of large arrays of floating bodies for ocean wave energy extraction." Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/104198.

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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2016.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 257-263).
Ocean wave energy is a large, and mostly untapped potential source of renewable energy worldwide. The scope of engineering solutions for harvesting wave energy is vast, ranging from wave-induced oscillating bodies, to overtopping devices and oscillating water columns. One particularly interesting approach to energy harvesting is to use arrays of oscillating bodies. The advantage of such a solution lies in potential amplification of the wave field through the interactions of waves that are diffracted and radiated by the bodies. Recent examples from other fields of physics (e.g. photonics crystals) show that by carefully engineering the configuration of the array, it is possible to greatly improve its performance. This thesis studies the performance of large arrays of axisymmetric bodies through the use of multiple scattering formulation of wave interactions. The focus is on the energy extraction characteristics in particular, but the effects on mean drift force are also studied. The multiple scattering (MS) formulation for Wave Energy Converter (WEC) arrays is extended in three areas. First, the dynamical behavior of a body in an array is decoupled from the dynamics of the array as a whole. This allows for the dynamical characteristics of a body to be completely determined in isolation, and then used in an array setting through newly-formed dynamical transfer matrices. This approach is especially beneficial in optimization studies, where the changes in the spatial array configuration do not require the recalculation of the hydrodynamic characteristics of an array. Second, the non-linear mean drift force on an array is expressed in terms of newly-formed non-linear drift transfer matrices. Lastly, a theoretical formulation is developed for periodic arrays with closely-spaced rows of bodies so that they can be analyzed in an exact manner within the MS formulation. Based on these extensions, a fast computational algorithm is developed that is capable of handling large arrays (0(100) bodies) of different configurations (general finite-size arrays, periodic arrays, periodic arrays of subarrays). The algorithm imposes no constraints on the body-size-to-wavelength ratio or on the inter-body spacings. Using this algorithm, a series of systematic studies of energy extraction characteristics by different array configurations is performed (as a function of wavenumber and wave incoming angle). These array configurations can be described with at most two parameters. In particular, the study of periodic and uniformly spaced line arrays reveals that large gains occur before new scattering orders appear (at Rayleigh wavelength). The gains are particularly large for super-resonant wavenumbers where there is still significant energy extraction. The studies of rectangularly arranged arrays show that, while still related to Rayleigh wavelengths, the optimal spacing is governed by the emergence of higher scattering orders. In all cases, arrays arranged in the direction of array propagation (attenuator arrays) perform poorly, except for sub-resonant wavenumbers. The effect or spacing irregularity (linear, quadratic and random) is studied on terminator arrays. The performance of irregularly spaced arrays as a function of wavenumber is more uniform, without high peaks in performance, and it indicates that there is a trade-off between high array gain and broad-bandedness of array gain. Finally, optimization of spatial configuration of a series of large arrays (up to 200 bodies) is performed. The array configuration is parameterized such that it can be described by a small number of variables, but that still allows a large number of different configuration types (irregularities in body spacings). Gradients of objective functions (extracted energy, array gain, drift force) are obtained using the adjoint method that, by also employing matrix-free matrix-vector multiplications, leads to a fast, memory-efficient gradient-based optimization algorithm. The optimization is performed for regular and irregular seas. The optimized rectangular arrays lead to high array gains, especially for mildly super-resonant wavenumbers where it reaches values of over 4. Surprisingly, uniformly spaced rectangular arrays perform better than the irregularly spaced ones in both regular and irregular seas. For many optimized arrays, the array capture width (extraction cross-section) is equal to the geometrical extent (cross-section) of the array, indicating that these arrays harvest all the energy of a particular frequency incoming on the spatial area they occupy. The optimal configurations are analyzed from a physical standpoint and compared to other structured arrays in physics. The results overall provide guidelines on the possible future design of WEC arrays.
by Grgur Tokić.
Ph. D.

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Noad, Imogen Frances. "Absorbing power from ocean waves : a mathematical approach to modelling wave energy converters." Thesis, University of Bristol, 2018. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.752773.

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Du, Qingjie, and 杜青杰. "Numerical study of the hydrodynamic performance of a point-absorbing wave energy converter." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2011. http://hub.hku.hk/bib/B47152849.

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As fossil energy is depleting and global warming effect is worsening rapidly, developing renewable energies becomes the top priority in most countries. In recent years, wave energy has attracted more and more attention due to its high energy density and enormous global capacity. The goal of this study is to carry out a numerical study of the hydrodynamic performance of a point-absorbing wave energy converter. In this study, an accurate and efficient numerical wave fume was established first. Commercial software code FLUENT?, which is a state-of-the-art computer program package for modeling fluid flow and heat transfer, was used for the numerical simulation. Based on the Navier-Stokes equations for viscous, incompressible fluid and Volume of fluid (VOF) method, a numerical wave tank was developed. Dynamic meshing method was used to simulate the wavemaker, and Geo-Reconstruct scheme was used to capture and reconstruct the free surface. A wave-absorbing method employing porous medium model was proposed to act as the wave absorbing beach, which can absorb the wave energy efficiently. A series of regular waves were simulated using the proposed numerical method. Validation has been made by physical experiments. After developing the wave flume model, a cylinder, which represents the point-absorbing wave energy converter (WEC), was added into the wave flume. The hydrodynamic behavior of the WEC was studied. The numerical results were also compared with physical experiments. Based on the numerical simulation results, suggestions on optimizing the point-absorber are provided. In this study, eight wave cases, with different wave period and wave length were simulated. The results show that the numerical simulation can match well with the physical wave tank result. Both the wave height and wave period in different cases can match well between the numerical simulation and physical wave tank results. In the wave-cylinder simulation, the results also show a good match in the numerical study and physical study. This numerical model is very significant in ocean structure design. The cylinder tested in this study can be easily changed to a ship or an offshore-platform. Compared with the physical experiment, numerical simulation is more flexible. The simulation can be carried on a large time span and spatial scale. The geometry can be changed easily. Also the cost of numerical simulation is relatively cheap compared with the physical experiment.
published_or_final_version
Mechanical Engineering
Master
Master of Philosophy

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30

Alsahlawi, Saad. "Development of a floating wave energy converting breakwater for gulf type marine environment." Thesis, University of Nottingham, 2018. http://eprints.nottingham.ac.uk/49372/.

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With the increase in human activity associated with the recent rise in Kuwait’s oil production, there is greater need for an optimised solution to protect the Kuwaiti coastline and islands from wave attacks and erosion. This thesis describes a programme of research conducted to support the development of a cost-effective method of protecting the Kuwaiti coastline with a breakwater system that also provides an opportunity to generate energy by locally increasing the energy density of waves to make wave energy conversion (WEC) more efficient, cost-effective and commercially competitive. A comprehensive review of the historical development and current state-of-the-art regarding breakwater and WEC technologies is presented. On the basis of these evaluations, a floating breakwater combined with point absorber device is identified as appropriate for use in the Kuwaiti near shore marine environment. The need for increasing the local energy density at the point absorber is highlighted and the concept of using a parabolic concentrator in combination with point absorber is suggested and developed. An analytical study extends the understanding of the role of damping in the response of an idealised point absorber device. A steady-state harmonic model is developed to simulate the motion of a single buoy with one degree of freedom (heave) along the vertical axis to optimise its geometrical and control parameters and maximise its power absorption from incident waves. Evaluating different buoy shapes namely: bullet, spike, and bi-cone (60o/120o) indicates that for each buoy shape, there is an optimum operating range for the power take-off (PTO) that drives the generator where wave energy capture and thus electrical power would be greatest. In the model, comprising a spring-damper system, the PTO is represented as a damper with a constant damping coefficient (〖 c〗_1) and the radiation force is represented by a linear radiation damping term (〖 c〗_2). The model reveals that the best performance is obtained at the optimum value for c_1 which is c_1= c_2=k/ω. This condition is met when the buoy with optimum mass is at resonance with the peak frequency of the sea state at ω^2=k/m. Evaluating the power absorption as a function of 〖 c〗_2 in the model also reveals that at resonance, a buoy of any shape will have two types of behaviour: one driven by low radiation damping and the other by high radiation damping range of values. Operation in the low 〖 c〗_2 region is difficult to achieve in practice, and hence, it is recommended that devices should be designed to operate in the high 〖 c〗_2 region to maximise power capture. Data is presented from wave tank testing conducted using a flume at the Kuwaiti Institute for Scientific Research (KISR). This is used to evaluate the capability of the proposed parabolic concentrator elements to increase potential wave energy harvesting. A wealth of data, both visualisation and numerical, was obtained and this compares well with the computational analyses. The results indicate that a parabola-buoy system would be capable of absorbing almost 260 kW of power at prototype scale (1:16). A computational modelling approach using the commercial CFD code ANSYS-Fluent is developed, applying the volume of fluid approach combined with a wave boundary condition. The KISR wave tank was modelled with parabolic element installed and data is compared to that obtained experimentally. Good agreement between CFD and experimental data is obtained validating the modelling choices made. Additional modelling results for the behaviour of waves near an anchored buoy in combination with a parabolic concentrator are presented. The work presented in this thesis shows that there is the potential for substantial benefit for power absorption through using a combined parabolic concentrator-point absorber device. Future modelling work with fluid-structure interaction and moving buoy will permit further optimisation and development paving the way for full-scale developments in the future.

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Helfrich, L. Cody. "Estimating oceanic internal wave energy from seismic reflector slope spectra." Laramie, Wyo. : University of Wyoming, 2008. http://proquest.umi.com/pqdweb?did=1594476671&sid=1&Fmt=2&clientId=18949&RQT=309&VName=PQD.

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32

Ashton, Ian Gerard. "Spatial variability of wave fields over the scale of a wave energy test site." Thesis, University of Exeter, 2011. http://hdl.handle.net/10036/3471.

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Accurate wave measurements are required for wave energy applications, including resource assessments and performance assessments. In response, wave data are measured from deployment sites, commonly using wave buoys or other point wave sensors. Spatial variability in the wave field will introduce inaccuracies to the analysis of data captured from a single point to represent a separate location or area. This thesis describes research undertaken to quantify the effect of spatial variability on the accuracy of direct wave measurements taken at a wave energy site. An array of four timesynchronised wave buoys were deployed, separated by 500m, in a location close to the Wave Hub wave energy test site in Cornwall, UK. These data were subject to close scrutiny in terms of data processing and quality control, which raised specific issues regarding data processing and the validation of wave data for a new measurement facility. Specific recommendations are made for data captured from this facility, and bespoke quality control routines were developed. This process minimises the possible contribution of errors to the processed data, which is observed to be of the highest importance when analysing simultaneous data sets, and provides a data set that is particularly suited to the examination of the spatial characteristics of ocean waves. The differences between simultaneous data demonstrated local physical processes to be causing a deterministic difference between the waves at the measurement sites, which contributed to a significant difference between the power statistics at different locations within the site. Instantaneous differences between measurements were observed to agree well with theoretical estimations of random error, based on sampling theory. The culmination of the research is a unique analysis of the spatial properties of ocean wave fields on the scale of a wave energy test site, of direct relevance to the development and monitoring of wave energy test sites.

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Defne, Zafer. "Multi-criteria assessment of wave and tidal power along the Atlantic coast of the southeastern USA." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/33864.

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The increasing demand for energy and the increased depletion rate of nonrenewable energy resources call for research on renewable alternatives. Mapping the availability of these resources is an important step for development of energy conversion projects. For this purpose, the wave power potential along the Atlantic coast of the southeastern USA, and the tidal stream power along the coast of Georgia are investigated in this study. Wave power potential is studied in an area bounded by latitudes 27 N and 38 N and longitudes 82 W and 72 W (i.e. North Carolina, South Carolina, Georgia, and northern Florida). The available data from National Data Buoy Center wave stations in the given area are examined. Power calculated from hourly significant wave heights and average wave periods is compared to power calculated using spectral wave energy density. The mean power within 50 km of the shore is determined to be low, whereas higher power is available further offshore beyond the 3500 m contour line. The tidal stream power potential along the coast of the state of Georgia is evaluated based on the NOAA tidal predictions for maximum tidal currents and three dimensional numerical modeling of the currents with Regional Ocean Modeling System (ROMS). The modeling results are validated against the available measurements. This region has low to moderate average tidal currents along most of the coast, but with the possibility of very strong local currents within its complex network of tidal rivers and inlets between barrier islands. Tidal stream power extraction is simulated with a momentum sink in the numerical models at the estuary scale to investigate effect of power extraction on the estuarine hydrodynamics. It is found that different power extraction schemes might have counterintuitive effects on the estuarial hydrodynamics and the extraction efficiency. A multi-criteria method that accounts for the physical, environmental and socioeconomic constraints for tidal power conversion schemes is proposed to select favorable locations and to rank them according to their suitability. For this purpose, the model results are incorporated into a Geographical Information System (GIS) database together with other geospatial datasets relevant to the site selection methodology. The methodology is applied to the Georgia coast and the candidate areas with potential are marked.

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Lejerskog, Erik. "Theoretical and Experimental Analysis of Operational Wave Energy Converters." Doctoral thesis, Uppsala universitet, Elektricitetslära, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-274635.

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This thesis studies wave energy converters developed at Uppsala University. The wave energy converters are of point absorbing type with direct driven linear generators. The aim has been to study generator design with closed stator slots as well as offshore experimental studies. By closing the stator slots, the harmonic content in the magnetic flux density is reduced and as a result the cogging forces in the generator are reduced as well. By reducing these forces, the noise and vibrations from the generator can be lowered. The studies have shown a significant reduction in the cogging forces in the generator. Moreover, by closing the slots, the magnetic flux finds a short-cut through the closed slots and will lower the magnetic flux linking the windings. The experimental studies have focused on the motion of the translator. The weight of the translator has a significant impact on the power absorption, especially in the downward motion. Two different experiments have been studied with two different translator weights. The results show that with a higher translator weight the power absorption is more evenly produced between the upward and downward motion as was expected from the simulation models. Furthermore, studies on the influence of the changing active area have been conducted which show some benefits with a changing active area during the downward motion. The experimental results also indicate snatch-loads for the wave energy converter with a lower translator weight. Within this thesis results from a comparative study between two WECs with almost identical properties have been presented. The generators electrical properties and the buoy volumes are the same, but with different buoy heights and diameters. Moreover, experimental studies including the conversion from AC to DC have been achieved. The work in this thesis is part of a larger wave power project at Uppsala University. The project studies the whole process from the energy absorption from the waves to the connection to the electrical grid. The project has a test-site at the west coast of Sweden near the town of Lysekil, where wave energy systems have been studied since 2004.

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Easton, Matthew Colin. "An assessment of tidal energy and the environmental response to extraction at a site in the Pentland Firth." Thesis, University of the Highlands and Islands, 2013. https://pure.uhi.ac.uk/portal/en/studentthesis/an-assessment-of-tidal-energy-and-the-environmental-response-to-extraction-at-a-site-in-the-pentland-firth(0ada05c2-3f33-463d-8f92-c9faad77a614).html.

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Shelf tidal streams are accelerated by coastal features, such as headlands and islands. In the search for sustainable forms of electricity generation, such locations may become attractive for tidal stream power. For many prospective sites, however, little is known about the intricacies of the local tidal dynamics: knowledge which is crucial to understanding the resource and the potential environmental consequences of its extraction. This thesis explores tidal stream energy in the Pentland Firth (Scotland, UK). This channel contains some of the most promising tidal stream energy sites in the world and is set to become host to the first large-scale arrays of tidal stream turbines, but its detailed characteristics were previously unknown. A hydrodynamic model was used to investigate the complex tidal dynamics of the Pentland Firth. This demonstrated, for the first time, the hydrodynamic mechanisms driving the exceptionally fast tidal currents through this channel. The model was then refined at a key site within the Pentland Firth, the Inner Sound. The results provided insight into complex flow characteristics, such as displacement and misalignment of peak flood and ebb tides, which must be considered when contemplating the exploitation of this energy resource. Tidal stream turbines were simulated in the hydrodynamic model. Artificial energy extraction was parameterised at the sub-grid-scale via added seabed drag. Turbine drag of varying magnitude was represented by a novel analytical model based on published characteristics of horizontal axis turbines. This new formulation reflects the non-linear dynamics of tidal turbine operation. Using the new turbine model, arrays of turbines were simulated within the Inner Sound. Complex interactions between the dynamics of energy extraction and flow required individual turbines to be parameterised in-concert with all other turbines in the array. This required extra effort, but offered enhanced insight into the behaviour of turbine arrays. Accounting for nonlinear turbine dynamics at high current speeds limited the magnitude of peak energy dissipation. Tidal stream velocities decreased both upstream and downstream of the extraction zone and were accelerated around it. At peak energy extraction, changes in tidal velocity were detectable several kilometres from the array, but were confined to the shallow waters of the Inner Sound and its environs. Implications for array modelling are discussed in the context of environmental impact assessments.

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Joubert, J. R. "An investigation of the wave energy resource on the South African Coast, focusing on the spatial distribution of the South West coast." Thesis, Link to the Internet, 2008. http://hdl.handle.net/10019.1/351.

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Lindroth, [formerly Tyrberg] Simon. "Buoy and Generator Interaction with Ocean Waves : Studies of a Wave Energy Conversion System." Doctoral thesis, Uppsala universitet, Elektricitetslära, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-160085.

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On March 13th, 2006, the Division of Electricity at Uppsala University deployed its first wave energy converter, L1, in the ocean southwest of Lysekil. L1 consisted of a buoy at the surface, connected through a line to a linear generator on the seabed. Since the deployment, continuous investigations of how L1 works in the waves have been conducted, and several additional wave energy converters have been deployed. This thesis is based on ten publications, which focus on different aspects of the interaction between wave, buoy, and generator. In order to evaluate different measurement systems, the motion of the buoy was measured optically and using accelerometers, and compared to measurements of the motion of the movable part of the generator - the translator. These measurements were found to correlate well. Simulations of buoy and translator motion were found to match the measured values. The variation of performance of L1 with changing water levels, wave heights, and spectral shapes was also investigated. Performance is here defined as the ratio of absorbed power to incoming power. It was found that the performance decreases for large wave heights. This is in accordance with the theoretical predictions, since the area for which the stator and the translator overlap decreases for large translator motions. Shifting water levels were predicted to have the same effect, but this could not be seen as clearly. The width of the wave energy spectrum has been proposed by some as a factor that also affects the performance of a wave energy converter, for a set wave height and period. Therefore the relation between performance and several different parameters for spectral width was investigated. It was found that some of the parameters were in fact correlated to performance, but that the correlation was not very strong. As a background on ocean measurements in wave energy, a thorough literature review was conducted. It turns out that the Lysekil project is one of quite few projects that have published descriptions of on-site wave energy measurements.

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Bliss, Nice Sam. "Qualitative risk analysis on wave energy technologies." Thesis, Uppsala universitet, Institutionen för elektroteknik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-423092.

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Wave energy as an industry is yet to emerge as a reliable energy technology. As of now, no wave energy device is said to be a commercial success. Survival in the harsh ocean environment, the low frequency of waves and the variability of wave resources are the basic challenges that a wave power concept or a developer has to overcome. In addition to these challenges, there are number of other barriers such as economic and regulatory risks which hinder the development. A number of concepts or devices have failed one after another, to be commercially successful. Many of the failures were due to economic reasons and others were due to technical or environmental factors. Mistakes or failures can be repeated if they are not shared within the industry. This thesis attempts to identify the barriers to wave energy concepts and to analyse them qualitatively. Efforts have been taken to include the previous instances of failures and their causes so as to avoid them in future. The data was collected through literature review of published papers, reports, news articles and through a survey which was distributed among experts in the industry and academia. It can be seen that one barrier can trigger others and that they are interconnected. In the same way, solving one barrier can clear the others too. The risks faced by wave energy technologies are identified, analysed and some mitigation methods are discussed.

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Chatzigiannakou, Maria Angeliki. "Efficiency evaluation of the offshore deployments of wave energy converters and marine substations." Licentiate thesis, Uppsala universitet, Elektricitetslära, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-335184.

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Yang, Xiufeng. "Ocean current energy resource assessment for the United States." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/50352.

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Ocean currents are an attractive source of clean energy due to their inherent reliability, persistence and sustainability. The Gulf Stream system is of particular interest as a potential energy resource to the United States with significant currents and proximity to the large population on the U.S. east coast. To assess the energy potential from ocean currents for the United States, the characterization of ocean currents along the U.S. coastline is performed in this dissertation. A GIS database that maps the ocean current energy resource distribution for the entire U.S. coastline and also provides joint velocity magnitude and direction probability histograms is developed. Having a geographical constraint by Florida and the Bahamas, the Florida Current has the largest ocean current resource which is fairly stable with prevalent seasonal variability in the upper layer of the water column (~200m). The core of the Florida Current features higher stability than the edges as a result of the meandering and seasonal broadening of the current flow. The variability of the Gulf Stream significantly increases as it flows past the Cape Hatteras. The theoretical energy balance in the Gulf Stream system is examined using the two-dimensional ocean circulation equations based on the assumptions of the Stommel model for quasi-geostrophic subtropical gyres. Additional turbine drag is formulated and incorporated in the model to represent power extraction by turbines. Parameters in the model are calibrated against ocean observational data such that the model can reproduce the volume and kinetic energy fluxes in the Gulf Stream. The results show that considering extraction over a region comprised of the entire Florida Current portion of the Gulf Stream system, the theoretical upper bound of averaged power dissipation is around 5.1 GW, or 45 TWh/yr. If the extraction area comprises the entire portion of the Gulf Stream within 200 miles of the U.S. coastline, the theoretical upper bound of averaged power dissipation becomes approximately 18.6 GW or 163 TWh/yr. The impact of the power extraction is primarily constrained in the vicinity of the turbine region, and includes a significant reduction of flow strength and water level drop in the power extraction site. The turbines also significantly reduce residual energy fluxes in the flow, and cause redirection of the Gulf Stream. A full numerical simulation of the ocean circulation in the Atlantic Ocean is performed using Hybrid Coordinate Ocean Model (HYCOM) and power extraction from the Florida Current is modeled as additional momentum sink. Effects of power extraction are shown to include flow rerouting from the Florida Strait channel to the east side of the Bahamas. Flow redirection is stronger during peak summer flow resulting in less seasonal variability in both power extraction and residual fluxes in the Florida Current. A significant water level drop is shown at the power extraction site, and so is a slight water level rise along the coasts of Florida and the Gulf. The sum of extracted power and the residual energy flux in the Florida Current is lower than the original energy flux in the baseline case, indicating a net loss of energy reserve in the Florida Current channel due to flow redirection. The impact from power extraction on the mean flow field is concentrated in the near field of the power extraction site, while shifts in the far flow field in time and space have little impact on the overall flow statistics.

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Barnabè, Paola. "Analysis of Wells Turbine for a specific wave energy converter." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2020.

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Vista la crescita della popolazione globale ed il conseguente aumento del fabbisogno di energia è necessaria una transizione verso forme di energie rinnovabili e sostenibili. Gli oceani e le coste del mondo, costituenti fondamentali di quello che è il 'Blue World' sono componenti chiave del capitale ambientale del pianeta e del suo capitale economico. Solo quando si imparerà a sfruttare questo tipo di risorse questa transizione sarà possibile ed efficace per l'intera popolazione globale. Ecco perché l'elaborato finale tratta l'analisi di una turbina di tipo Wells per i convertitori di energia dalle onde del mare e degli oceani.

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Jarocki, Dmitri. "Wave Energy Converter Performance Modeling and Cost of Electricity Assessment." DigitalCommons@CalPoly, 2010. https://digitalcommons.calpoly.edu/theses/278.

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California is experiencing a rapid increase in interest for the potential of converting ocean waves into clean electricity. Numerous applications have been submitted for the permitting of such renewable energy projects; however the profitability, practicability, and survivability have yet to be proven. Wave energy conversion technology has steadily matured since its naissance in the 1970’s, several wave energy power installations currently exist, and numerous plans for commercial power plant are in the works on the shores of multiple continents. This study aims to assess the economic viability of two proposed commercial wave energy power plant projects on the Central California Coast. A theoretical 25 MW capacity wave energy plant located at a site five nautical miles off of Point Arguello, in Santa Barbara County is compared to a site five nautical miles off of Morro Bay, in the County of San Luis Obispo. The Pacific Gas and Electric Company and Green Wave Energy Solutions, LLC have proposed full-scale commercial wave power plants at these sites, and are currently undergoing the federal permitting processes. Historical wave resource statistics from 1980 to 2001 are analyzed with performance specifications for the AquaBuOY, Pelamis P1, and WaveDragon wave energy converters (WECs) to calculate the annual electrical output of each device at each site. Sophisticated computer modeling of the bathymetric influence on the wave resource at each site is presented using the program Simulating Waves Nearshore (SWAN) developed by the Delft University of Technology. The wave energy flux, significant wave height, and peak period are computed at each site for typical summer and winter swell cases, using seafloor depth measurements at a 90 meter rectangular grid resolution. The economic viability of commercial electricity generation is evaluated for each WEC at each site by the calculation of the net present value of an estimated 25-year project life-cycle, the internal rate of return, and the required cost of electricity for a 10-year project simple payback period. The lowest required price of electricity is $0.13/kWh and occurs at the Point Arguello site using the AquaBuOY WEC. The highest annual capacity factor is 18% using the Pelamis WEC. The net present value and internal rate of return calculations suggest that the AquaBuOY WEC is profitable at both sites for electricity prices above $0.14/kWh. Shallow water wave propagation SWAN modeling demonstrated favorable wave energy flux states for WEC operation and power generation at both sites, with typical winter energy fluxes of 30-37 kW/m.

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Engström, Jens. "Hydrodynamic Modelling for a Point Absorbing Wave Energy Converter." Doctoral thesis, Uppsala universitet, Elektricitetslära, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-160319.

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Surface gravity waves in the world’s oceans contain a renewable source of free power on the order of terawatts that has to this date not been commercially utilized. The division of Electricity at Uppsala University is developing a technology to harvest this energy. The technology is a point absorber type wave energy converter based on a direct-driven linear generator placed on the sea bed connected via a line to a buoy on the surface. The work in this thesis is focused mainly on the energy transport of ocean waves and on increasing the transfer of energy from the waves to the generator and load. Potential linear wave theory is used to describe the ocean waves and to derive the hydrodynamic forces that are exerted on the buoy. Expressions for the energy transport in polychromatic waves travelling over waters of finite depth are derived and extracted from measured time series of wave elevation collected at the Lysekil test site. The results are compared to existing solutions that uses the simpler deep water approximation. A Two-Body system wave energy converter model tuned to resonance in Swedish west coast sea states is developed based on the Lysekil project concept. The first indicative results are derived by using a linear resistive load. The concept is further extended by a coupled hydrodynamic and electromagnetic model with two more realistic non-linear load conditions. Results show that the use of the deep water approximation gives a too low energy transport in the time averaged as well as in the total instantaneous energy transport. Around the resonance frequency, a Two-Body System gives a power capture ratio of up to 80 percent. For more energetic sea states the power capture ratio decreases rapidly, indicating a smoother power output. The currents in the generator when using the Two-Body system is shown to be more evenly distributed compared to the conventional system, indicating a better utilization of the electrical equipment. Although the resonant nature of the system makes it sensitive to the shape of the wave spectrum, results indicate a threefold increase in annual power production compared to the conventional system.

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Crossley, George Robert Northcote. "Quantification of uncertainty in sub-sea acoustic measurement, and validation of wave-current kinematics, at a tidal energy site." Thesis, University of Edinburgh, 2018. http://hdl.handle.net/1842/31541.

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As developers seek to convert the energy of the tides into electricity, sub-sea turbines must be designed to perform well in increasingly harsh conditions. Such energetic seas have historically been avoided, hence measurements taken below the surface in strong tidal currents and large waves are relatively few, and the theory behind these interactions is underdeveloped. This thesis compares measurements of subsurface velocity taken in the field, at a UK site proposed for development, to the velocity outputs of a model capable of combining waves and currents in a number of ways. In particular the interaction between waves and currents is investigated. The methodology incorporates a novel virtual velocity measurement instrument to measure the model flow, replicating the physical instruments used at sea, such that direct comparisons can be made between the two data-sets. Model and field velocities show good agreement across a range of current speeds and wave heights, with a range of metrics used to demonstrate the suitability of the model, based on linear wave-current theory, for this site. The wave-current interaction module is calibrated, with linear superposition of wave and current velocities proving a suitable representation of field velocities. Calculation of a dispersion relationship affected by mean current velocity marginally improves calibration with field data. Analysis of other sites using the tools developed will further validate this type of model, which in combination with blade element momentum theory, is able to predict pre-construction site specific loads on tidal turbines. Doppler Current Profilers (DCPs) are able to measure subsurface water particle kinematics and sea surface elevation simultaneously, however assumptions made by these instruments jeopardise detail when recording in highly energetic seas, particularly where waves and turbulent tidal currents combine. Models developed to optimise the design of tidal turbines require correct site specific inputs to accurately reflect the conditions that a turbine may encounter through its lifetime, moreover, the kinematics of these models must be accurately validated. To overcome the limitations in DCP measurements a 'Virtual' Doppler Current Profiler (VDCP) is developed (Crossley et al. 2017), enabling quantification of error in site characteristics, and 'like for like' comparisons of field and model kinematics that has never previously been documented. The numerical model developed incorporates tidal currents, waves and turbulence combined linearly to output subsurface velocity based on conditions from the field which have been averaged over ten minute intervals. The inputs are simple, time averaged characteristics (current magnitude, direction, and profile; wave height, period and direction, turbulence intensity and turbulence length-scale) and the model outputs velocities over a two dimensional grid that develops with time. The VDCP samples this flow as if it were the very instrument in the field that recorded the data used for validation. Taking into account the heading, pitch and roll of the instrument a data set directly comparable to that measured in the field is generated. The VDCP is initially used in quantifying error in wave and turbulence statistics, demonstrating a phase dependency of velocity measurements averaged between beams and providing a theoretical error for wave and turbulence characteristics sampled under a range of conditions, in order to improve tidal site characterisation. Spectral moments of the subsurface longitudinal wave orbital velocities recorded by the VDCP can be between 0.1 and 9 times those measured at a point for certain turbulent current conditions, turbulence intensity measurements may vary between 0.2 and 1.5 times the input value in low wave conditions and turbulence length scale calculations can vary by over ten times the input value, dependent on both current and wave conditions. The methodology can be used to determine a theoretical error in any site characterisation parameter for any set of wave, current and turbulence conditions. Results of the model validation using the VDCP show that the tidal flow model, and in particular the newly developed wave-current interaction module, is effective in simulating field subsurface velocities over a range of depths, for waves of up to 3m significant wave height and currents of up to 3.5ms-1. The model is effective in reproducing the wave climate using both measured and modelled surface elevation spectra, and tests, with marginal improvements, the effect of modifying the dispersion equation to account for currents. Field and model velocities compare well over the frequency range dominated by waves, showing only small underestimations in model standard deviations with respect to those from field data, at depths close to the sea surface. At the low frequency end of the modelled spectra, where large turbulent eddies dominate, there is some deviation in model accuracy, particularly during the ebb tide where recorded turbulence parameters are extremely variable, creating uncertainty due to a relatively small sample size. Between field and model velocity maxima, some scatter is observed, potentially providing uncertainty in the estimation of ultimate loads. Model and field damage equivalent velocities, used in the determination of fatigue loads, agree well. Results suggest that a linear wave-current representation of subsurface velocities at this particular tidal site is applicable. Care should be taken when interpreting this result due to the relatively small sample size, and the possibility of site specific nuances, and as such further studies are proposed. The Virtual DCP model is a novel development which has proven its usefulness in the work contained in this thesis and in the analysis of commercial field data. It is extremely versatile, adapting to a range of configurations and set up criteria such that it can be used in the quantification of DCP measurement error for a range of flow characteristics. This information is useful in the design of tidal turbines (and other sub-sea structures) as well as for oceanographic and biological processes. The tidal flow model developed extends beyond the capability of similar numerical models with the capability to model the interaction between waves and currents according to a number of different options. Combined with the VDCP, which samples from the model flow field, a system is created that can be effectively calibrated to find the best model solution to replicate flows at a tidal site measured by a 'real' DCP over a broad range of sea conditions and water depths. The purpose is to ensure that models used to predict the sub surface velocities in the field are suitable and a key question was to understand whether the linear super-position of linear wave models and a turbulent current flow provides a realistic model of the particle kinematics with a view to undertaking loads analysis of a tidal stream turbine. Comparisons of this kind have not previously been documented, and this thesis lays out the path to improved site characterisation.

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Castellucci, Valeria. "Sea Level Compensation System for Wave Energy Converters." Doctoral thesis, Uppsala universitet, Elektricitetslära, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-295603.

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The wave energy converter developed at Uppsala University consists of a linear generator at the seabed driven by the motion of a buoy on the water surface. The energy absorbed by the generator is negatively affected by variations of the mean sea level caused by tides, changes in barometric pressure, strong winds, and storm surges. The work presented in this doctoral thesis aims to investigate the losses in energy absorption for the present generation wave energy converter due to the effect of sea level variations, mainly caused by tides. This goal is achieved through the modeling of the interaction between the waves and the point absorber. An estimation of the economic cost that these losses imply is also made. Moreover, solutions on how to reduce the negative effect of sea level variations are discussed. To this end, two compensation systems which adjust the length of the connection line between the floater and the generator are designed, and the first prototype is built and tested near the Lysekil research site. The theoretical study assesses the energy loss at about 400 coastal points all over the world and for one generator design. The results highlight critical locations where the need for a compensation system appears compelling. The same hydro-mechanic model is applied to a specific site, the Wave Hub on the west coast of Cornwall, United Kingdom, where the energy loss is calculated to be about 53 %. The experimental work led to the construction of a buoy equipped with a screw jack together with its control, measurement and communication systems. The prototype, suitable for sea level variations of small range, is tested and its performance evaluated. A second prototype, suitable for high range variations, is also designed and is currently under construction. One main conclusion is that including the compensation systems in the design of the wave energy converter will increase the competitiveness of the technology from an economic point of view by decreasing its cost per kWh. The need for a cost-effective wave energy converter with increased survivability emphasizes the importance of the presented research and its future development.

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Vermaak, Rieghard. "Development of a novel air-cored permanent magnet linear generator for direct drive ocean wave energy converters." Thesis, Stellenbosch : Stellenbosch University, 2013. http://hdl.handle.net/10019.1/80267.

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Thesis (PhD)--Stellenbosch University, 2013.
ENGLISH ABSTRACT: In hierdie tesis word ’n nuwe lug kern permanent magnet (PM) lineêre generator (LG) vir toepassing tot direk aangedrewe (DA) oseaan golf energie omsetters (GEO) ontwikkel. Die nuwe LG word ontwikkel vanaf die lineêre dubbel-kant topologie in ’n poging om probleme met die huidige longitudinale vloed (LV) yster kern LGs, wat tot dusvêr oorheersend voorkom in eksperimentele DA-GEOs, te oorkom. Die grootste probleem met hierdie LGs is die masiewe aantrekkings kragte tussen hul yster stators en die PM transleerders. ’n Groot hoeveelheid strukturuele staal word benodig om die luggaping te handhaaf, terwyl die las op die laars ook ’n groot probleem is. Die nuwe LG gebruik ’n lug kern stator wat alle aantrekkings kragte tussen die stator en transleerder elimineer en dus die nodige strukturuele material verminder. Die topologie van die transleerder is ook van so ’n aard dat die netto aantrekkings kragte op enige spesifieke PM ideaal nul is; dit verminder die strukturuele materiaal selfs verder. Die transleerder het ook ’n nuwe transversale vloed pad wat die sogenaamde paarwyse vloed koppeling wat in LV-LGs voorkom, en die negatiewe effekte daarvan, verhoed. ’n Aantal nuwe bydraes tot die veld van LGs vir DA-GEO word in hierdie tesis gemaak. ’n Nuwe topologie lug kern PMLG is ontwikkel soos bespreek. Dit sluit in die ontwikkeling van analitiese en eindige element modelle en ’n optimerings prosedure wat vinnig optimale dimensies vir minimum aktiewe massa van die nuwe LG vind. In die ontwerp word dit ook gevind dat die drywingsdigtheid van LGs verbeter kan word deur zero oorvleuling tussen die die stator en transleerder by die slag endte toe te laat. ’n 1 kW prototipe van die nuwe LG word ontwerp en gebou; die uitvoerbaarheid van die konstruksie vir die nuwe topologie op ’n klein skaal word dus gedemonstreer. ’n Unieke toets opstelling word ook ontwerp en is gebasseer op bestaande toerusting in die vorm van ’n wind turbine generator en rug-aan-rug spannings bron omsetters. Met die toets opstelling word ’n enkel frekwensie golf ge-emuleer om die teorie en simulasies te verifieer en word ook ’n voorspellende beheer strategie geimplementeer, wat vir die eerste keer gedemonstreer word vir LGs vir DA-GEOs. Goeie ooreenstemming tussen die gemete en gesimuleerde data bevestig die voorgestelde modellerings en ontwerps metodes.
AFRIKAANSE OPSOMMING: In this thesis, a novel air-cored permanent magnet (PM) linear generator (LG) is developed with application to direct drive (DD) wave energy converters (WECs). The novel LG is developed from the linear double-sided topology in an attempt to overcome the problems with current longitudinal flux (LF) iron-cored LGs, which have so far been dominant in experimental DD-WECs. The biggest problem with these LGs is the massive attraction forces between their iron stators and PM translators. A large amount of structural steel is required to maintain the air gap, while the load on the bearings is also a large concern. The novel LG uses an air-cored stator which eliminates any attraction forces between the stator and translator and hence reduces the required structural material. Furthermore, the topology of the translator is such that the net attraction force on any particular PM is ideally zero, which even further reduces the structural material required for the translator. A new transverse circulating flux path is also introduced in the translator which prevents pair-wise flux coupling and its negative effects as observed in LF-LGs. A number of new contributions are made to the field of LGs for DD-WECs in this thesis. A novel topology aircored PMLG is developed as described. This includes the development of analytical and finite element models and an exhaustive optimisation procedure for quickly finding optimal dimensions for minimum active mass of the novel LG. In the design it is also found that the power density of LGs can be improved by allowing zero overlap between the stator and translator at the stroke ends. A 1 kW prototype of the novel LG is designed and built; the feasibility of constructing the novel LG on a small scale is as such demonstrated. A unique test rig is designed based on existing equipment in the form of a wind turbine generator and back-to-back voltage source converters. The test rig allows emulation of a monochromatic wave for verifying the theory and simulations and also allows for implementation of a predictive control strategy, which is for the first time demonstrated for LGs for DD-WECs. Good agreement between measured and simulated data confirms the presented modelling and design methods.

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Duman, Cagatay. "Evaluation And Comparison Of The Wave Energy Potential In Selected Coastal Regions In Turkey." Master's thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12612626/index.pdf.

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In order to meet energy needs in world, studies on wave energy, alternative energy, are becoming more and more important with each passing day. The purpose of this study is to identify the wave energy potential along the coastline of Turkey. For this purpose, the data of wind speed and direction, swell and wind wave height, period and direction for certain duration with the six hours time intervals are obtained from ECMWF for the wind and wave climate computations. In order to compute the wind and wave climate at any selected coastal location, software is developed by Serhan Aldogan in his MSc thesis. By the help of the specifically developed software, for every location, by utilizing existing wind data, depending on geographical location of station, in the direction of energy thought to produce, by using calculated average wind speed of storm which is above the selected wind speed u0, characteristics (Hs
Tm) of the waves of this storm and power (P, W/m) per unit length will be calculated. The duration curves for power, Hs and T, can be obtained. The duration curve represents the occurrence of the parameter (wave height, wave period, wave energy or wave power). It can also be called occurrence curve or availability curve. From these curves, for various percentages of the total storm duration, P, Hs and T&rsquo
s values can be determined. Also, in the analysis, the shapes of these curves can provide important information about the available wave energy for the selected coasts.

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48

Joubert, James Rattray. "Design and development of a novel wave energy converter." Thesis, Stellenbosch : Stellenbosch University, 2013. http://hdl.handle.net/10019.1/85817.

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Thesis (PhD)--Stellenbosch University, 2013.
ENGLISH ABSTRACT: The design, development and evaluation of a novel wave energy converter (WEC) device, called the ShoreSWEC, in a South African port development is presented. Based on the device requirements, site selection criteria were specified and applied to identify a suitable deployment location. A wave modeling procedure was developed to determine the operational wave conditions and available wave power resource at the selected location. The site was found to have a low mean annual average resource of approximately 2.3 kilowatt per meter wave crest (kW/m) due to its relatively sheltered location. The wave model was further used to determine design storm conditions and a structural stability analysis of the device was conducted. Experimental tests were performed to evaluate the hydrodynamic conversion efficiency of a single chamber of the device at its most conservative orientation, under a variety of wave energy conditions. The effect of a floor incline and an additional chamber on the performance of the system was investigated. The incline improved efficiency for low wave heights, making it ideal for the low wave power resource conditions of the site, whilst the multi-chamber system experienced increased performance at high wave periods. A comparison between the ShoreSWEC and a conventional oscillating water column (OWC) WEC showed that the OWC extracted 72% more energy, highlighting the sensitivity of performance on device orientation. A three-dimensional (3D) numerical model of the experimental setup was developed. The numerical model provided comparable water surface elevations inside the flume and chamber, yet predicted significantly higher internal chamber pressures and overall efficiency. The electricity generation potential of a 10 chamber ShoreSWEC at the specified location, approximated from the experimental results and 11 years of hindcast wave data, was found to be 6 kW on average for a 15 kW capacity system. Results of this study highlighted the need for greater understanding of the hydrodynamic characteristics of a full length device. Experimental tests in a 3D wave basin on a scaled full length ShoreSWEC model are therefore recommended. Once conducted, South Africa will be one step closer to the deployment of the full scale SWEC device.
AFRIKAANSE OPSOMMING: Die ontwerp, ontwikkeling en evaluasie van ‘n unieke golfenergieomsetter (GEO), genaamd die ShoreSWEC, in ‘n Suid-Afrikaanse haweontwikkeling word aangebied. Terrein evaluasie kriteria, gebaseer op die omsettervereistes, is ontwikkel en toegepas om die mees belowende terrein te identifiseer. ‘n Golfmodeleringsprosedure is ontwikkel om die operasionele golfkondisies en beskikbare golfdrywinghulpbron te bepaal. Daar is gevind dat die terrein ‘n lae gemiddelde golfdrywing van bykans 2.3 kilowat per meter golfkruin het as gevolg van die beskutte ligging. Die golfmodel is verder gebruik om ontwerpstormkondisies te bepaal en ‘n stabiliteitsanalise was op die toestel struktuur uitgevoer. Eksperimentele toetse van verskeie golfenergie kondisies is gedoen om die hidrodinamiese omsettingseffektiwiteit van ‘n enkel kamer van die toestel te bepaal teen sy konserwatiefste orientasie. Die effek van ‘n vloerhelling en ‘n addisionele kamer op die uitsette van die sisteem is ondersoek. Die helling het effektiwiteit verbeter vir lae golfhoogtes wat dit ideaal maak vir die lae hulpbron by die terrein, terwyl die veelvoudige-kamer-sisteem beter gevaar het by hoë golfperiodes. ‘n Vergelyking tussen die ShoreSWEC en ‘n konvensionele ossilerende waterkolom (OWK) GEO het gewys dat die OWK 72% meer energie onttrek. Dit beklemtoon die sisteem se sensitiwiteit vir die inkomende golfrigting. ‘n Drie-dimensionele (3D) numeriese model van die eksperimentele opstelling is ontwikkel. Die numeriese model het aansienlik hoër drukke binne die kamer, en gevolglik algehele effektiwiteit, voorspel as die eksperimentele toetse. Die elektriese opwekkingskapasiteit van ‘n 10 kamer ShoreSWEC by die terrein, gebaseer op die eksperimentele resultate en 11 jaar se golfdata, is bereken as 6 kW gemiddeld vir ‘n 15 kW kapasiteit stelsel. Die bevindinge van hierdie studie het die behoefte aan ‘n beter begrip van die hidrodinamiese eienskappe van ‘n vollengte sisteem beklemtoon. Eksperimentele toetse in ‘n 3D golfbak op ‘n geskaleerde vollengte ShoreSWEC model word dus aanbeveel. Sodra dit voltooi is, sal Suid-Afrika een stap nader wees aan die ontplooiing van ‘n volskaalse SWEC toestel.

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49

Wypych, Matthew. "A study of radiated surface waves in the context of the capture of ocean wave energy." Thesis, University of Canterbury. Mechanical Engineering, 2012. http://hdl.handle.net/10092/7463.

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The current drive to find new low-carbon forms of electricity generation has intensified interest in capturing energy from ocean waves. The large range of devices currently proposed to fulfil this drive raises the question "What are the characteristics of an effective wave energy converter?". This thesis explores the design of a particular type of wave energy converter (WEC), namely the point absorber, by examining the properties and interactions of different types of surface waves. Current theory suggests that in order for a WEC to effectively absorb wave energy, it must also be an efficient wave radiator. The solutions to the Laplace equation in circular-cylindrical coordinates (known as circular waves) are used as point sources for the surface waves radiated from an oscillating body. The properties of circular waves provide guidelines with regard to the shape, movement and radiation properties required to make an effective WEC. The interactions of circular waves with plane waves also determines the theoretical optimum performance of a WEC in threedimensional wave fields. Limitations on the theoretical size of radiated waves are identified and linked to the size of the oscillating body. This establishes the connection between a body's displaced volume and its performance as a WEC. Practical experiments aimed at determining if the circular waves correspond to waves radiated by different oscillating bodies were completed. A method of consistently generating and measuring radial waves was developed and data recorded for a cylinder, sphere and flat plate oscillating vertically or horizontally. The results show that the circular-cylindrical models are accurate, providing the body is axisymmetric and oscillates either vertically, or horizontally with a small amplitude. The experiments also demonstrate the practical implications of radiating surface waves. This thesis advances the understanding of point absorber wave energy converters by identifying simple design guidelines that embody the underlying physics of surface waves. It also develops new methods for generating, measuring and analysing the waves radiated from an oscillating body.

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50

Helkin, Steven Alexander. "Design and optimization of a wave energy harvester utilizing a flywheel energy storage system." Master's thesis, University of Central Florida, 2011. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4774.

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This thesis details the design and optimization of a buoy used to collect renewable energy from ocean waves. The proposed buoy is a point absorber--a device that transforms the kinetic energy of the vertical motion of surface waves into electrical energy. The focus of the research is on the mechanical system used to collect the energy, and methods to improve it for eventual use in an actual wave energy harvester. A flywheel energy storage system was utilized in order to provide an improved power output from the system, even with the intermittent input of force exerted by ocean waves. A series of laboratory prototypes were developed to analyze parameters that are important to the success of the point absorb mechanical system. By introducing a velocity-based load control scheme in conjunction with flywheel energy storage, it was seen that the average power output by the prototype was increased. The generator load is controlled via a relay switch that removes electrical resistance from the generator--this sacrifices time during which power is drawn from the system, but also allows the buoy to move with less resistance. A simulation model was developed in order to analyze the theoretical wave absorber system and optimize the velocity threshold parameters used in the load control. Results indicate that the power output by the system can be substantially improved through the use of a flywheel energy storage control scheme that engages and disengages the electrical load based on the rotational velocity of the flywheel system. The results of the optimization are given for varying-sized generator systems input into the simulation in order to observe the associated trends.
ID: 030646228; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Thesis (M.S.M.E.)--University of Central Florida, 2011.; Includes bibliographical references (p. 111-114).
M.S.M.E.
Masters
Mechanical and Aerospace Engineering
Engineering and Computer Science
Mechanical Engineering; Computer Aided Mechanical Engineering Track

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Dissertations / Theses on the topic 'Ocean wave energy harvesting'

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